What does the dreaded "E" word mean, anyway

In short, if the traditionally "highest" of all triploblasts--the vertebrate line, including our exalted selves--appears in the fossil record at the same time as all other triploblastic phyla in the Cambrian explosion, and if the most anatomically simplified of all parasites can evolve (as an adaptation to local ecology) from a free-living lineage within the "higher," triploblastic phyla, then the biological, variational, and Darwinian meaning of "evolution" as unpredictable and nondirectional gains powerful support from two cases that, in a former and now disproven interpretation, once bolstered an opposite set of transformational prejudices.

As a final thought to contrast the predictable unfolding of stellar evolution with the contingent nondirectionality of biological evolution, I should note that Darwin's closing line about "this planet ... cycling on according to the fixed law of gravity;' while adequate for now, cannot hold for all time. Stellar evolution will, one day, enjoin a predictable end, at least to life on Earth. Quoting one more time from Britannica:

   The Sun is destined to perish as a white dwarf. But before that happens, it
   will evolve into a red giant, engulfing Mercury and Venus in the process.
   At the same time, it will blow away the earth's atmosphere and boil its
   oceans, making the planet uninhabitable.

The same predictability also allows us to specify the timing of this catastrophe--about 5 billion years from now! A tolerably distant future, to be sure, but consider the issue another way, in comparison with the very different style of change known as biological evolution. Earth originated about 4.6 billion years ago. Thus, half of our planet's potential history unfolded before contingent biological evolution produced even a single species with consciousness sufficient to muse over such matters. Moreover, this single lineage arose within a marginal group of mammals--the primates, which include about 200 of the 4,000 or so mammalian species. By contrast, the world holds at least half a million species of beetles. If a meandering process consumed half of all available time to build such an adaptation even once, then mentality at a human level certainly doesn't seem to rank among the "sure bets," or even the mild probabilities, of history.

We must therefore contrast the good fortune of our own evolution with the inexorable evolution of our nurturing Sun toward a spectacular climax that might make our further evolution impossible. True, the time may be too distant to inspire any practical concern, but we humans do like to muse and to wonder. The contingency of our evolution offers no guarantees against the certainties of the Sun's evolution. We shall probably be long gone by then, perhaps taking a good deal of life with us and perhaps leaving those previously indestructible bacteria as the highest mute witnesses to a stellar expansion that will finally unleash a unicellular Armageddon. Or perhaps we, or our successors, will have colonized the universe by then and will shed only a brief tear for the destruction of a little cosmic exhibit entitled "the museum of our geographic origins." Somehow I prefer the excitement of wondering and cogitation--not to mention the power inherent in acting upon things that can be changed--to the certainty of distant dissolution.